This invention relates to a frame for an opening provided in an aircraft fuselage.
FIGS. 1 to 3 show by way of example the front of an aircraft 10 that comprises a fuselage 12 in which an opening 14 is made that makes it possible, for example, for passengers to pass, and said opening that separates the outside of the aircraft 16 from the interior environment 18 is able to be sealed by a door called a passenger door.
In a known manner, the fuselage of an aircraft comprises a skin 20 that is reinforced by a structure that comprises in particular a first series of longitudinal stiffeners (stringers) and a second series of transverse stiffeners (frames).
To provide the uptake of forces between the structure of the door and the structure of the fuselage, a door frame 22 is provided around the opening 14.
At the door frame 22, a passenger door induces primarily radial forces that are oriented toward the outside of the aircraft (indicated by the arrow F in FIG. 3); said forces are taken up by stops 24 provided at the frame 22.
For taking up such a type of force, the frame 22 comprises, on the one hand, an edge frame that comprises an upper longitudinal stiffener called a lintel 26, a lower longitudinal stiffener called a threshold 28, vertical stiffeners 30 on both sides of the opening 14, and, on the other hand, a secondary frame that consists of at least two vertical stiffeners 32 that are arranged on both sides of the opening at a certain distance and two upper and lower longitudinal stiffeners 34 that are distant from the lintel 26 and the threshold 28. Ribs or reinforcements are provided to connect the edge frame and the secondary frame. Thus, the stiffeners 30 and 32 are connected by ribs called intercostal ribs 36 in such a way as to form a ladder-shaped structure on both sides of the opening 12. The document WO03/104080 describes such a ladder-shaped structure.
As illustrated in FIG. 3, the moment generated by the shearing force F that is applied at each stop 24 on the frame 22 is taken up by two opposing reactions, a first reaction R1 at the secondary frame and a second reaction R2 at the edge frame. According to this type of design, the balancing of the forces is done locally opposite each door stop using a corresponding intercostal rib.
The loading of the door frame 22 is not limited to these radial forces. In a general manner, the door frame is to ensure the integrity of the fuselage.
According to a first embodiment, all of the elements that constitute the door frame 22 and the skin of the fuselage are metal, whereby the vertical stiffeners 30 and 32 as well as the intercostal ribs 36 are made from thick panels that are machined in a conventional manner. After machining, these different elements are assembled in such a way as to form the substructures in a ladder, and then the skin is next placed on these thus formed substructures. Starting from a metal skin, this solution has the drawback of comprising numerous attachments and has the advantage of having good control of the thickness and successive deposition planes that are parallel to one another.
So as to reduce the on-board weight of the aircraft, there is a tendency to use composite materials.
A first variant embodiment of a door frame made of composite material consists in making a first subassembly that comprises the edge frame, the secondary frame, and the intercostal ribs. The production of this subassembly in a single piece requires a complex device. Furthermore, the assembly with a composite material skin requires the use of wedges because of the contraction of the skin achieved from pre-impregnated folds that lead to greatly increasing the assembly time.